Copper red frits and pigments comprising silica and at least one of cupric oxide and cuprous oxide

ABSTRACT

This invention relates to lead free and cadmium free copper-containing glass fits that can be used as pigments to color other glass fits or to impart color to solid substrates such as glass, ceramic or metals, or to impart color to a thermoplastic mass. The compositions comprise silica, alkali metal oxides, alkaline earth metal oxides, tin oxide and copper oxide. The resulting compositions can be used to decorate and protect automotive, beverage, architectural, pharmaceutical and other glass substrates, generally imparting a red color.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to low-firing, high durability glass and enamelcompositions. In particular, the invention relates to glass fritcompositions, and the glasses, ceramics and enamels made therefrom,which include SiO₂, alkali metal oxides, alkaline earth metal oxides,tin oxide and copper oxide. The compositions possess a red colorachievable without the use of cadmium, lead, or chromium. Thecompositions may be used to form red-colored articles or as pigments onsubstrates such as glass, enamels, metals, and even as colorants inthermoplastics.

2. Description of Related Art

Coloration of glasses, enamels, metals and plastics with a red color haspresented an especially difficult challenge for skilled practitioners.Traditionally, one or more of the oxides of iron or lead or chromium orsulfides of cadmium have been used to impart a red color to suchsubstrates. For example, iron oxide, Fe₂O₃, lead oxide Pb₂O₃, andcadmium selenium sulfide ((Cd, Se)S), and such as molybdenum chromiumred, or pigment red 104. However, iron oxides often have unwanted sideeffects, and heavy metals such as lead, chromium (especially hexavalentchromium), cadmium and selenium have come under increasing scrutiny fromenvironmental agencies.

Further, most of the aforementioned red-tone pigments impart arelatively brownish color that often overwhelms the true red color oftendesired. There has been a dearth of truly deep vivid reds in the glassand enamels industry as well as in the thermoplastic industry.

Accordingly, and in particular, the goal of this work is to stainreduced-tin frits with copper to produce red pigments. Since cadmium isconsidered to be a heavy metal, replacing cadmium-containing pigmentswith cadmium-free pigments has long been an objective of the glassindustry.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a range of low firing, high durability glasses,glass frits, and glass enamel compositions that impart a red color toglass panels, enamel coatings, plastics, and other substrates. Theinvention describes the use of a red copper ruby glass as a pigment forthe decoration of glass, metal, ceramic, glass ceramic and tiles byscreen printing, spraying or digital printing. A distinguishing featureof the invention is the avoidance of cadmium (and lead) in pigments andto make cadmium free red. A red copper glass is used as a pigment. Thepigments are made by melting and annealing a glass that contains tin andcopper. Particles or clusters of metallic copper are formed in a redoxreaction between copper ions and tin ions:2Cu⁺+Sn²⁺→2Cu+Sn⁴⁺The copper ions are reduced by tin ions in an annealing step.

The pigment alone or in combination with a glass frit is used as adecoration color, and may be applied to a substrate by e.g., printing,brushing, dipping, rolling, or spraying. A substrate decorated with thepigment is then fired to fuse the pigment to the substrate, therebypermanently affixing the color thereto.

Using the pigments, glass frits and methods of the invention, it ispossible to obtain a red color on glass, metal, or ceramic substrates,using a cadmium-free formulation. Screen printing, spraying, orthermoplastic printing can be used to apply the pigment. Indirectprinting procedures involving decals are also envisioned. The pigmentsherein can also be used to directly color plastics. Where appropriate, asingle firing cycle can be used to impart a red color to substrates suchas glass, metals, and ceramics. Certain embodiments involve separatefiring and annealing steps, or more than one firing step.

Also it is possible to use also the unannealed frit as a forehearthcolorant. In this case the frit is added to a mass of molten glass inthe feeder channel. Glass objects, especially bottles, flasks ortumblers; are then formed, and the objects are subjected to heattreatment so that they develop a red color.

The invention also includes methods of making the various red glass fitsand pigments disclosed herein, either (a) smelting a red frit or (b)annealing a previously fired reducing frit with a copper compound (e.g.,copper sulfate, copper nitrate, etc.), that provides copper ions, whichexchange with those in the reducing frit. In (b), the copper compoundmay be combined with the reducing glass before the reducing glass isfritted as well.

In particular, the invention provides a fired enamel composition that isfree of lead, cadmium, bismuth, iron, selenium, arsenic, tantalum andsulfides, the composition comprising a solids portion comprising a fritportion, wherein the frit portion comprises, prior to firing: (a) 50-75wt % SiO₂, (b) 4-22 wt % R₂O, wherein R is at least one of Na and K, (c)2-30 wt % R′O wherein R′ is at least one of Mg, Ca, Sr and Ba (d) 0.5-20wt % B₂O₃, (e) 0-15 wt % Al₂O₃, (f) 1-15 wt % SnO, and (g) 1-10 wt %Cu₂O. When applied to and fired on a suitable substrate such as glass,enamel or metal, the inventive frit imparts a red color thereto.

In another embodiment, the invention relates to a fired enamelcomposition that is free of intentionally added lead, cadmium, bismuth,iron, selenium, arsenic, tantalum, chromium and sulfides, thecomposition comprising a solids portion comprising a fit portion,wherein the frit portion comprises, prior to firing: (a) 55-75 wt %SiO₂, (b) 8-22 wt % R₂O, wherein R is at least one of Na and K (c) 2-10wt % CaO, (d) 1-5 wt % MgO, (e) 0.1-3 wt % Al₂O₃, (f) 1-15 wt % SnO, and(g) 0.05-1 wt % SO₃.

In another embodiment, the invention relates to an enamel compositionthat is free of intentionally added: lead, cadmium, bismuth, iron,selenium, arsenic, tantalum, chromium and sulfides, the compositioncomprising a solids portion comprising a fit portion, wherein the fitportion comprises, prior to firing (a) 60-75 wt % SiO₂, (b) 8-20 wt %Na₂O, (c) 8-20 wt % K₂O, (d) 1-15 wt % SnO, 5-15 wt % CaO, and 1-5 wt %Cu₂O.

Yet another embodiment of the invention involves a method of decoratinga glass substrate comprising: (a) applying to a glass substrate, ceramicsubstrate or metal substrate an enamel composition that is free ofintentionally added: lead, cadmium, bismuth, iron, selenium, arsenic,tantalum, chromium and sulfides, the composition comprising a solidsportion, wherein the solids portion comprises a frit portion, whereinthe frit portion comprises, prior to firing: (i) 50-75 wt % SiO₂, (ii)4-22 wt % R₂O, wherein R is at least one of Na and K, (iii) 3-15 wt %CaO, (iv) 0-15 wt % MgO, (v) 0.5-20 wt % B₂O₃, (vi) 0-15 wt % Al₂O₃,(vii) 1-15 wt % SnO, and (viii) 1-10 wt % Cu₂O, and (b) firing thesubstrate and enamel composition at a temperature sufficient to flow theenamel composition to cause the enamel composition to at least partiallyadhere to the glass substrate.

Yet another embodiment of the invention involves a method of decoratinga glass substrate comprising: (a) applying to a glass substrate anenamel composition that is free of intentionally added: lead, cadmium,bismuth, iron, selenium, arsenic, tantalum, chromium and sulfides, thecomposition comprising a solids portion, wherein the solids portioncomprises a frit portion, wherein the frit portion comprises, prior tofiring: (i) 60-75 wt % SiO₂, (ii) 8-20 wt % Na₂O, (iii) 8-20 wt % K₂O,(iv) 1-15 wt % SnO, (v) 5-15 wt % CaO, and (vi) 1-5 wt % Cu₂O, and (b)firing the substrate and enamel composition at a temperature sufficientto flow the enamel composition to cause the enamel composition to atleast partially adhere to the glass substrate.

Still another embodiment of the invention is a method of decorating aglass substrate comprising: (a) applying to a glass substrate an enamelcomposition that is free of intentionally added: lead, cadmium, bismuth,iron, selenium, arsenic, tantalum, chromium and sulfides, thecomposition comprising a solids portion, wherein the solids portioncomprises a frit portion, wherein the frit portion comprises, prior tofiring: (i) 55-75 wt % SiO₂, (ii) 8-22 wt % R₂O, wherein R is at leastone of Na and K, (iii) 2-10 wt % CaO, (iv) 1-5 wt % MgO, (v) 0.1-3 wt %Al₂O₃, (vi) 1-15 wt % SnO, and (vii) 0.05-1 wt % SO₃, (b) firing thesubstrate and enamel composition at a temperature sufficient to flow theenamel composition to cause the enamel composition to at least partiallyadhere to the glass substrate, (c) applying to the fired enamelcomposition a blend of copper sulfate and sodium sulfate, and (d) firingand annealing the blend of copper sulfate and sodium sulfate to effectcopper ion exchange with sodium ions in the enamel composition to imparta red color thereto.

Yet another embodiment of the invention is a particulate red pigmentcomposition including a glass frit and copper particles or copperclusters.

Another embodiment of the invention is a particulate red pigmentcomposition including a glass frit including copper ions and tin ions.

Still another embodiment of the invention is a method of decorating asubstrate comprising: (a) applying to the substrate a coating of anenamel composition that is free of intentionally added: lead, cadmium,bismuth, iron, selenium, arsenic, tantalum, chromium and sulfides, thecomposition comprising a solids portion, wherein the solids portioncomprises a frit portion comprising, prior to firing: (i) 60-75 wt %SiO₂, (ii) 8-25 wt % (Li₂O+Na₂O+K₂O), (iii) 1-15 wt % SnO, (iv) 5-15 wt% CaO, (v) 1-15 wt % MgO (vi) 0.1-2 wt % Fe₂O₃, 0.1-2 wt % Cu₂O and0.05-1 wt % SO₃, and (b) firing the substrate and coating at atemperature sufficient to flow the enamel composition to cause theenamel composition to adhere to the substrate.

In general, embodiments of the invention relate to methods of decoratinga substrate with a red color comprising applying any enamel or pigmentcomposition disclosed herein to the substrate and firing the substrate.

Still another embodiment of the invention is a method of decorating athermoplastic comprising (a) forming a red-colored enamel compositionenamel composition that is free of intentionally added: lead, cadmium,bismuth, iron, selenium, arsenic, tantalum, chromium and sulfides, thecomposition comprising a solids portion comprising a fit portion,wherein the frit portion comprises, prior to firing: (i) 50-75 wt %SiO₂, (ii) 8-25 wt % R₂O, wherein R is at least one of Li, Na and K,(iii) 2-30 wt % R′O, wherein R′ is at least one of Mg, Ca, Sr and Ba,(iv) 0.1-10 wt % of at least one of Cu₂O and CuO, and (v) 0.1-5 wt %SO₃, and (b) blending the enamel composition with a thermoplastic massto form a red-colored thermoplastic mass.

Still another embodiment of the invention is a mass of molten glass thatis free of intentionally added lead, cadmium, bismuth, iron, selenium,arsenic, tantalum, chromium and sulfides, the molten glass comprising:(a) 50-75 wt % SiO₂, (b) 4-22 wt % R₂O, wherein R is at least one of Naand K, (c) 2-30 wt % R′O, wherein R′ is at least one of Mg, Ca, Sr andBa, (d) 0.5-20 wt % B₂O₃, (e) 1-15 wt % SnO, and (f) 1-10 wt % of atleast one of Cu₂O and CuO, wherein a partial pressure of oxygen in themolten mass of less than 10⁻⁹ atmospheres. The above molten glass fritcould be used as a feeder frit to stain a mass of molten base glass witha partial pressure of oxygen greater than 10⁻⁴ to less than 10⁻¹atmospheres.

A method of manufacturing red glass comprising adding a coloring fit, toa mass of molten colorless glass in a feeder channel, forming glassobjects from the molten mass of glass, then subjecting the glass objectsto heat treatment so that they develop a red color. This methodpreferably involves a frit that is free of lead, cadmium, bismuth, iron,selenium, arsenic, tantalum, chromium and sulfides, and wherein thecomposition comprises, prior to melting: (i) 50-75 wt % SiO₂, (ii) 4-22wt % R₂O, wherein R is at least one of Na and K, (iii) 2-30 wt % R′O,wherein R′ is at least one of Mg, Ca, Sr and Ba, (iv) 0.5-20 wt % B₂O₃,(v) 1-15 wt % SnO, and (vi) 1-10 wt % of at least one of Cu₂O and CuO.

In the aforementioned method, and others disclosed herein, the partialpressure of oxygen in the molten mass of the coloring frits accordingthe invention is less than 10⁻⁹ atmospheres. In the aforementionedmethod, and others disclosed herein, the partial pressure of oxygen inthe mass of molten colorless glass (that is being colored) has a partialpressure of oxygen in the range of 10⁻⁴ to 10⁻¹ atmospheres, andpreferably between 10⁻³ and 10⁻² atmospheres.

Further embodiments of the invention include (a) copper containing(copper oxide) pigment; (b) copper cluster (islands of copper metal)containing pigment; (c) copper cluster containing pigment also includingat least one of gold or silver; (d) a method of decorating a substratesuch as glass, metal, ceramic, porcelain, bone china, glass ceramic,tiles or plastic using a red copper ruby glass as a pigment; (e) amethod of decorating a substrate such as glass, metal, ceramic,porcelain, bone china, glass ceramic or tiles by screen-printing: directand/or indirect (decal), spraying or digital printing; (f) a method ofchanging the color shade of a colored under layer which is white, yellowor blue or other colors. It is appreciated that copper oxide may beprovided in the form of cuprous oxide (Cu₂O) and cupric oxide (CuO).Other copper salts and copper compounds like CuSO₄, CuCO₃ or (CH₃CO₂)₂Cucould be also used.

The frits, pigments, enamels and other solids of the invention are freeof lead, cadmium, bismuth, iron, selenium, arsenic, tantalum, chromiumand sulfides. In various embodiments the frits, pigments, enamels andother solids may be (a) absolutely devoid of such metals, (b) free ofintentional additions of such metals, and/or (c) contain only traceamounts, for example, less than 1 wt %, less than 0.5 wt %, less than0.1 wt %, less than 0.01 wt %, and all values in between.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the present inventionmay be employed.

DETAILED DESCRIPTION OF THE INVENTION

Enamel compositions of the invention include a glass frit portion, whichin turn includes a combination of the oxides of silicon, at least onealkali-metal oxide, at least one alkaline-earth metal oxide, copperoxide, iron oxide, tin oxide, and boron oxide.

Alternatively, another embodiment of the invention involves enamelcompositions of the invention include a glass frit portion, which inturn includes a combination of the oxides of silicon, at least onealkali-metal oxide, at least one alkaline-earth metal oxide, and tinoxide. The foregoing frit may be applied to a substrate, fired, and thencoated with a blend of copper sulfate and sodium sulfate. The sulfateblend may be heated and annealed to effect copper ion exchange with thesodium in the earlier fired layer or into the substrate (if it is asodium containing glass or enamel). Alternatively, copper nitrate may beused as a supply of copper ions, in which case the additional sodium (assupplied by sodium nitrate above) may not be necessary.

The components of the inventive compositions, articles and methods aredetailed hereinbelow. Compositional percentages are by weight. Certainembodiments of the invention are envisioned where at least somepercentages, temperatures, times, and ranges of other values arepreceded by the modifier “about.” “Comprising” is intended to providesupport for “consisting of” and “consisting essentially of.” Where theclaims of this PCT application do not find explicit support in thespecification, it is intended that such claims provide their owndisclosure as support for claims or teachings in a later filed nationalapplication. All compositional percentages are by weight and are givenfor a blend prior to firing. Numerical ranges of oxides or otheringredients that are bounded by zero on the lower end (for example, 0-10wt % SnO) are intended to provide support for the concept “up to [theupper limit],” for example “up to 10 wt % SnO” as well as a positiverecitation that the ingredient in question is present in an amount thatdoes not exceed the upper limit. An example of the latter is “comprisesSnO, provided the amount does not exceed 10 wt %.” A recitation such as“8-25 wt % (Li₂O+Na₂O+K₂O)” means that any or all of Li₂O, Na₂O and/orK₂O may be present in an amount of 8-25 wt % of the composition.

All ranges disclosed herein are to be understood to encompass thebeginning and ending range values and any and all subranges therein. Forexample, a stated range of “1 to 10” should be considered to include anyand all subranges between (and inclusive of) the minimum value of 1 andthe maximum value of 10; that is, all subranges beginning with a minimumvalue of 1 or more and ending With a maximum value of 10 or less, e.g.,1.0 to 2.7, 3.3 to 8.9, 5.7 to 10, etc. Details on each ingredientfollow.

Frit (Glass) Component. The principal glass and enamel compositionsherein include. In particular, the invention provides an enamelcomposition comprising a solids portion comprising a fit portion,wherein the fit portion comprises, on weight percentages, the ranges ofoxides presented in Table 1.

TABLE 1 Ranges of Oxides Formula Oxide I II III IV V VI VII VIII SiO₂50-75  50-70  55-68 55-75  55-70 60-75  62-72 65-70 (R₂O) 4-22 8-2010-17 8-22 10-20 Na₂O 0.3-18  3-15  5-12 9-20 10-18 8-20 12-18 14-18 K₂O2-10 4-8  4-8 2-13  4-10 8-20 12-18 14-18 (R′O) 0-30 CaO 0-15 4-12  5-102-10 4-9 5-15  7-13  8-12 MgO 0-15 2-12 3-8 1-5  1.5-4  B₂O₃ 0.5-20 5-15  7-14 9-17 11-15 Al₂O₃ 0-15 1.5-12   2-10 0.1-3   0.5-2.5 SnO 1-152-12 1-15  2-13 1-15  3-12  5-10 Cu₂O 1-10 2-4  2.5-4  — — 0.1-5  0.5-3   1-2.5 SO₃ 0.05-1    Type Red Red Red Reducing Reducing Red RedRed

When applied to and fired on a suitable substrate such as glass, enamelor metal, the inventive frits impart a red color thereto. For thereducing frits, (containing tin but no copper) such fit is applied toand fired on a substrate followed by application and annealing of acopper composition providing copper ions to exchange with sodium in thefirst fired fit. For example, a combination of copper sulfate and sodiumsulfate may be applied to a previously fired reducing frit. It isenvisioned that oxide ranges from different columns can be combined; theembodiments of invention are not limited to the oxides recited in onecolumn.

The constituents in parentheses (R₂O) and (R′O) are generic formulasrepresenting alkali metal oxides (Na₂O and K₂O; also Li₂O in someembodiments) and alkaline earth metal oxides (MgO, CaO, SrO, and BaO),respectively. An embodiment may be limited both by the amount of thegeneric formula or the amount of the specific formula or both. “Opt”means that in a broadest embodiment, the noted oxide is optional,meaning an independent claim covering the oxides of a column need notcontain such optional oxide.

The invention envisions two main procedures to formulate and apply apigment to a substrate which imparts a red color thereto.

In a first procedure, all oxides are blended and melted together at900-1500° C. to form a clear melt that is quickly cooled to roomtemperature. Optionally in this first procedure an organic reducingagent such as sugar, potassium sodium tartrate or other organic reducingagent(s) may be blended and melted together to form the clear melt.Reducing sugars may contain an acetal group or a hemi-acetal group.Certain ketoses, those which tautomerize to aldoses, are reducingsugars. Reducing sugars include dextrose (glucose), maltose, sucrose,and certain glucopyranosides, for example. Carbon black as reducingagent is also possible. A red color is developed by annealing at400-750° C. A variation hereon is to bypass cooling to room temperature,and instead cool from firing temperatures directly to annealingtemperatures in the 400-750° C. range, thereby developing the red color.In either case, a red-colored frit is produced that can be used as apigment. Such embodiments are found in columns I-III and VI-VII in Table1.

In a second procedure, a tin-containing (reducing) fit (as in columns IVand V in Table 1) is smelted, frilled and fired to form a reducingglass. A copper sulfate/sodium sulfate paste is applied to the reducingglass and heated to 400-700° C. Copper ions diffuse into the reducingfrit thereby imparting a red color thereto, forming a red frit that canbe used as a pigment. Excess salts are washed away with water.

Following either of the two aforementioned procedures, the so-formed redpigment frit may be milled to any desired particle size between 0.1 to100 microns, preferably 0.1-50 microns, more preferably 0.1-35 microns,still more preferably 0.1-20 microns, yet more preferably 0.1-10microns, even more preferably 0.1-5 microns. In alternate embodiments,the D₉₀ size is 35 microns, preferably 20 microns, more preferably 10microns and most preferably 5 microns. If the frit is used as a feederfrit, it may, but need not be, milled. If it is not milled, it may haveparticle sizes in the millimeter range.

The red pigment, which is really a glass frit, may be red or colorless,may be called a concentrate frit or feeder frit, may be applied directlyto a substrate absent a carrier frit, or may be used in conjunction withanother fit. This other fit may be non-colored, to adjust the intensityof the color so imparted. Also the chemical resistance and thermalexpansion coefficient could be impacted by such a frit. It is alsopossible to change the transparency by using an opaque frit and tochange the color shade by using a colored frit. Application of thepigment to a substrate is facilitated by use of a medium, which includesa binder and a solvent to disperse and wet the pigment, and ensurehomogeneous coating of the pigment on the substrate prior to firing.

If colors other than red are desired, or minor alterations to the redcolors obtained by the inventive frits and pigments are desired,additional oxides can be added to any embodiment herein, singly, or inany combination, up to the noted weight percentage: Cs₂O: 2%; Ag₂O: 5%;MgO: 5%; CeO₂: 5%; MnO: 10%; NiO 5%; P₂O₅: 5%; V₂O₅: 10%; La₂O₃: 5%;Pr₂O₃: 5%; In₂O₃: 5%; Cr₂O₃: 5%; Sb₂O₃: 5%, CoO: 5%; Nb₂O₅: 4%; WO₃: 4%;and MoO₃: 4%. Generally, Mn gives a brown color, Ni and Cr each givegreen colors, and Co gives a blue color.

As can be seen above, the composition of the glass frits useful in thisinvention can be adapted over a broad range of oxide compositions.Glasses may be formulated according to the principal glass and enamelcompositions above, together with, optionally one or more secondary oradditional oxides. The glass and enamel compositions herein typicallycontain low amounts of metals such as chromium, iron, lead, cadmium,bismuth, selenium, arsenic, tantalum, and sulfides. Preferably, theglass compositions herein contain less than 5 wt % of each of chromium,iron, lead, cadmium, bismuth, selenium, arsenic, tantalum, and sulfidesand more preferably, less than 1 wt % of each. Still more preferably,less than 0.5 wt % of each is present, and even more preferably, lessthan 0.1 wt % of each is present. Most preferably, the glass and enamelcompositions herein are substantially free of, or devoid theaforementioned metals or their oxides. It is recognized that constraintsof commerce sometimes limit the purity of metal or oxide constituentsused in smelting a glass frit. Hence, embodiments of the inventioninclude those frit compositions where each or all of the metals are notintentionally added. Still more preferably, the glass frit compositionsherein and the enamels made therefrom are absolutely devoid of chromium,iron, lead, cadmium, bismuth, selenium, arsenic, and tantalum, as wellas sulfides in any form.

Broadly, the glass frits and enamels useful herein have melting pointsin the range of about 1000° F. to 1400° F. (about 540° C. to about 760°C.), or any intermediate temperature such as 1030° F., 1040° F., 1050°F., 1060° F., 1080° F., 1110° F., 1150° F., 1190° F., 1200° F., 1210°F., 1250° F., 1275° F., 1300° F., 1325° F., 1350° F., and 1375° F., andvarious of the frits may be effectively fired at those temperatures.Preferably, the glass frits herein can be fired at 1000-1250° F., morepreferably at 1020-1200° F., still more preferably at about 1030-1150°F., and most preferably at about 1040-1100° F. Container glass istypically not fired above 1200° F. (650° C.).

Generally, the glass frits are formed in a known manner, for example,blending the starting materials (oxides, salts) and melting together ata temperature of about 1000 to about 1400° C. (about 1830 to about 2550°F.) for about 45 minutes to about several hours to form a molten glasshaving the desired composition. The molten glass formed can then besuddenly cooled in a known manner (e.g., water quenched) to form a frit.The frit can then be ground using conventional milling techniques to afine particle size as desired.

Standard fits or fluxes can be used to dilute the inventive fits andpigments, for example transparent fluxes sold under the Samba®trademark. As Samba® 10-1600, 10-1650 and 10-1641, with softening pointsof 640, 660 and 680° C., respectively. Ferro Frits from the NPR system,lead-free glass enamels suitable for tableware, including NPR 820, whichis a non-colored flux, may also be used. The Samba® and NPR system fitsnoted herein are commercially available from Ferro Corporation,Cleveland, Ohio, United States.

Crystalline Material. Crystalline materials may, but need not, beincluded along with the frit compositions herein to promotecrystallization (i.e., crystallization seeds). Crystalline materialsuseful herein include zinc silicates, zinc borates, zinc titanates,silicon zirconates, aluminum silicates, calcium silicates, andcombinations thereof. The crystalline materials may include, withoutlimitation, Zn₂SiO₄, 2ZnO.3TiO₂, ZnTiO₃, ZnO.B₂O₃, 3ZnO.B₂O₃,5ZnO.2B₂O₃, and Al₂SiO₅. The commonly owned Rüderer, U.S. Pat. No.5,153,150 and Sakoske, U.S. Pat. No. 5,714,420 patents provide furtherinformation on crystalline materials. Preferred crystalline materialsinclude zinc silicates such as Zn₂SiO₄ and zinc borosilicates such asZnO.B₂O₃. Specific examples of seed materials used herein includeproduct numbers 2077 (bismuth silicate seed material) and 2099 (zincsilicate seed material) manufactured by Ferro Glass and ColorCorporation of Washington, Pa. The enamels herein may optionally include0.1-15 wt %, preferably about 0.5-10 wt %, and more preferably 1-5 wt %of at least one crystalline material.

Decoration and Glass Forming. A glass substrate may be colored ordecorated by applying any enamel composition described herein to atleast a portion of a substrate, for example, a glass substrate such as aglass sheet, automotive glass, (i.e., windshield), architectural glass,dinnerware, household appliance panels, beverage containers, tumblers,and bottles. An enamel composition may, but need not, be applied in theform of a paste as disclosed herein.

In particular, the invention involves a method of decorating a glasssubstrate comprising: (a) applying to the substrate a coating of anenamel composition comprising a solids portion, comprising a fritportion comprising, prior to firing: prior to firing: (i) 60-75 wt %SiO₂, (ii) 8-25 wt % (Li₂O+Na₂O+K₂O), (iii) 1-15 wt % SnO, (iv) 5-15 wt% CaO, (v) 2-10 wt % MgO (vi) 0.1-2 wt % Fe₂O₃, 0.1-2 wt % Cu₂O and 0.1wt % SO₃ and (b) firing the substrate and coating at a temperaturesufficient to flow the enamel composition to cause the enamelcomposition to adhere to the substrate.

The enamel composition may be applied to the entire surface of asubstrate, or to only a portion thereof, for example the periphery, or aportion corresponding to another desired decorative pattern.

The method may include a glass forming step whereby the glass substrateis heated to an elevated temperature and subjected to a forming pressureto bend the glass substrate. In particular, bending the glass substratemay involve heating the glass substrate to which has been applied the toan elevated temperature, of, for example, at least about 570° C., atleast about 600° C., at least about 625° C., or at least about 650° C.Upon heating, the glass is subjected to a forming pressure, e.g.,gravity sag or press bending in the range of 0.1 to 5 psi, or 1-4 psi,or typically about 2-3 psi, with a forming die.

One or more alternate glass forming steps to form beverage containers,tumblers, dinnerware and other glass articles may be included in themethods herein.

The following paragraphs relate to ingredients that facilitate handlingand application of the inventive glasses and pigments.

Organic Vehicle. When applied by procedures requiring one, such asscreen printing, the solid ingredients herein may be combined with anorganic vehicle, or medium, to form a paste. The paste in generalcontains 60-90 wt % solids, preferably 65-85%, more preferably 70-80 wt%, as above described and 10-40% of an organic vehicle, preferably15-35%, more preferably 20-30%. The viscosity of the paste is adjustedso that it can be screen-printed, roll coated, sprayed, or otherwiseapplied in a desired manner onto the desired substrate. Paste ratios mayfall in the ranges of about 1.4:1 to 5:1, or about 2:1 to 4.4:1.

Useful organic vehicles include Ferro Corporation 80 1022, which is awater-soluble medium displaying optimum combustibility anddepolymerization, suitable for all decorative, direct screen printingapplications on glass, enamel; ceramics and porcelain. It is alsosuitable for printing relief decors. Working viscosity for screenprinting is recommended to be 8.0-12.0 Pa*s (20° C., D=200 1/s,plate-cone-system), while that for roller coating is recommended to be aworking viscosity of 90-110 sec. (23° C., 6 mm DIN Cup).

The organic vehicle comprises a binder and a solvent, which are selectedbased on the intended application. It is essential that the vehicleadequately suspend the particulates (i.e., frit, pigment, crystallinematerial) and burn off completely upon firing. In particular, bindersincluding methyl cellulose, ethyl cellulose, and hydroxypropylcellulose, and combinations thereof, may be used. Suitable solventsinclude propylene glycol, diethylene glycol butyl ether; 2,2,4-trimethylpentanediol monoisobutyrate (Texanol™); alpha-terpineol; beta-terpineol;gamma terpineol; tridecyl alcohol; diethylene glycol ethyl ether(Carbitol™), diethylene glycol butyl ether (Butyl Carbitol™); pine oils,vegetable oils, mineral oils, low molecular weight petroleum fractions,tridecyl alcohols, and synthetic or natural resins and blends thereof.Surfactants and/or other film forming modifiers can also be included.The solvent and binder may be present in a weight ratio of about 50:1 toabout 20:1.

In general, the enamel pastes are viscous in nature, with the viscositydepending upon the application method to be employed and end use. Forpurposes of screen-printing, viscosities ranging from 10,000 to 80,000,preferably 15,000 to 35,000 centipoise, and more preferably 18,000 to28,000 centipoise at 20° C., as determined on a Brookfield Viscometer,#29 spindle at 10 rpm, are appropriate.

Dispersing Surfactant. A dispersing surfactant assists in pigmentwetting, when an insoluble particulate inorganic pigment is used. Adispersing surfactant typically contains a block copolymer with pigmentaffinic groups. For example, surfactants sold under the Disperbyk® andByk® trademarks by Byk Chemie of Wesel, Germany, such as Disperbyk 162and 163, which are solutions of high molecular weight block copolymerswith pigment affinic groups, and a blend of solvents (xylene,butylacetate and methoxypropylacetate). Disperbyk 162 has these solventsin a 3/1/1 ratio, while the ratio in Disperbyk 163 is 4/2/5. Disperbyk140 is a solution of alkyl-ammonium salt of an acidic polymer in amethoxypropylacetate solvent.

Rheological Modifier. A rheological modifier is used to adjust theviscosity of the green pigment package composition. A variety ofrheological modifiers may be used, including those sold under the Byk®,Disperplast®, and Viscobyk® trademarks, available from Byk Chemie. Theyinclude, for example, the BYK 400 series, such as BYK 411 and BYK 420,(modified urea solutions); the BYK W-900 series, (pigment wetting anddispersing additives); the Disperplast® series, (pigment wetting anddispersing additives for plastisols and organosols); and the Viscobyk®series, (viscosity depressants for plastisols and organosols).

Flow aid. A flow aid is an additive used to control the viscosity andrheology of a pigment or paste composition, which affects the flowproperties of liquid systems in a controlled and predictable way.Rheology modifiers are generally considered as being eitherpseudoplastic or thixotropic in nature. Suitable surfactants hereininclude those sold commercially under the Additol®, Multiflow®, andModaflow® trademarks by UCB Surface Specialties of Smyrna, Ga. Forexample, Additol VXW 6388, Additol VXW 6360, Additol VXL 4930, AdditolXL 425, Additol XW 395, Modaflow AQ 3000, Modaflow AQ 3025, ModaflowResin, and Multiflow Resin.

Adhesion promoter. Adhesion promoting polymers are used to improve thecompatibility between a polymer and a filler. Suitable adhesionpromoters include those sold by GE Silicones of Wilton, Conn. under theSilquest®, CoatOSil®, NXT®, XL-Pearl™ and Silcat® trademarks. Examplesinclude the following product numbers, sold under the Silquest®trademark: A1101, A1102, A1126, A1128, A1130, A1230, A1310, A162, A174,A178, A187, A2120. For example, Silquest® A-187 is(3-glycidoxypropyl)trimethoxysilane, which is an epoxysilane adhesionpromoter. Silanes sold by Degussa AG of Düsseldorf, Germany, under theDynasylan® trademark are also suitable.

Stabilizers. Light or UV stabilizers are classified according to theirmode of action: UV blockers—that act by shielding the polymer fromultraviolet light; or hindered amine light stabilizers (HALS)— that actby scavenging the radical intermediates formed in the photo-oxidationprocess. The compositions of the invention may, when advantageous,comprise about 0.1 to about 2 wt % of a light stabilizer, preferablyabout 0.5 to about 1.5%, and further comprise about 0.1 to about 4 wt %of a UV blocker, preferably about 1 to about 3%.

Light stabilizers and UV blockers sold under the Irgafos®, Irganox®,Irgastab®, Uvitex®, and Tinuvin® trademarks by from Ciba SpecialtyChemicals, Tarrytown, N.Y., may be used, including product numbers 292HP, 384-2, 400, 405, 411L, 5050, 5055, 5060, 5011, all using the Tinuvintrademark. Suitable UV blocking agents include Norbloc® 7966 (2-(2′hydroxy-5′ methacryloxyethylphenyl)-2H-benzotriazole); Tinuvin 123(bis-(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ester); Tinuvin 99(3-(2H-benzotriazole-2-yl) 5-(1,1-dimethylethyl)-4-hydroxybenzenepropanoic acid, C7-9-branched alkyl esters)Tinuvin 171 (2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methyl-phenol).Products sold under the Norbloc® trademark are available from JanssenPharmaceutica of Beerse, Belgium.

Suitable hindered amine light stabilizers (HALS) are sold by theClariant Corporation, Charlotte, N.C., under the Hostavin® trademark,including Hostavin 845, Hostavin N20, Hostavin N24, Hostavin N30,Hostavin N391, Hostavin PR31, Hostavin ARO8, and Hostavin PR25. HALS areextremely efficient stabilizers against light-induced degradation ofmost polymers. They do not absorb UV radiation, but act to inhibitdegradation of the polymer, thus extending its durability. Significantlevels of stabilization are achieved at relatively low concentrations.The high efficiency and longevity of HALS are due to a cyclic processwherein the HALS are regenerated rather than consumed during thestabilization process. They also protect polymers from thermaldegradation and can be used as thermal stabilizers

The inventive materials are cadmium-free red pigments that can be madeby conventional glass and pigment processing. The pigment can be used todecorate glass ceramic metal substrates and as colorant in paints andthermoplastic processing. The copper coatings and pigments can be usefulas UV blockers.

EXAMPLES

The following compositions represent exemplary embodiments of theinvention. They are presented to explain the invention in more detail,and do not limit the invention.

Example 1

TABLE 2 Tin-reducing frit formulations in wt % Oxide Frit F Frit G SiO₂70.36 65.75 CaO 8.53 7.96 Fe₂O₃ 0.48 0.45 MgO 3.68 3.43 SnO 6.59 12.72Na₂O 10.23 9.56 SO₃ 0.15 0.14

A reducing frit is pasted together with copper nitrate as follows(133B). One gram of Frit G and 1 g Cu(NO₃)₂ in DPG were weighed onto apane of auto glass. The components were mulled together with a spatula.The paste was spread out on the surface of the glass, and the glass wasdried on a hotplate. After drying, the panes were placed in a kiln setat 1120° F. and heated for four minutes. No red color was evident. Thepanes were moved to another kiln and the temperature was raised to 1250°F. The powder on the panes began to show more red value after heatingfor a few minutes at 1250° F., so the panes were left at thistemperature for 20 minutes. The panes were removed and cooled. Thepowder had an adobe color that is blue/dirty and weak compared tocadmium colors, but the red was identifiable.

When the samples were examined under the microscope, it appeared thatnot all of the glass particles were colored. This suggested that a moreintense color could be possible. The following sample was made: (133D)from 0.5 g 133B, 0.6 g Cu(NO₃)₂ in DPG, and 0.24 g 85% H₃PO₄.

The ingredients were mulled together on a glass pane with a spatula. Thepanes were placed on a hotplate and dried. The powder was loosened fromthe surface with a spatula. The panes were fired at 1250° F. After 10minutes, the color of the two powders was quite brown, but thisobservation was made while the powders were still hot. The two paneswere left in the kiln and the power was shut off. The two samples wereleft to cool until the morning. Upon cooling, the red value of both ofthese samples was increased. These two samples are darker in color thantheir parent samples. Of these two samples, 133D is a more saturatedcolor. Under microscopic examination, there were some colorlessparticles in this sample, but 99% or more of the material exhibited ared color.

TABLE 3 Exemplary Frit formulations in wt %. Formula Frit Frit Frit FritFrit Frit Frit Frit Oxide A B C D E F G H SiO₂ 65.38 59.58 54.56 51.4955.13 70.36 65.75 66.33 Na₂O 9.56 9.07 17.68 0.42 17.87 10.23 9.56 10.27K₂O 5.83 7.88 2.16 4.41 2.19 — — 9.05 CaO 9.31 8.49 3.76 8.99 3.80 8.527.96 9.46 MgO — — 3.25 — 3.28 3.68 3.43 — B₂O₃ 0.85 0.78 13.64 16.3213.78 — — 0.88 Al₂O₃ 3.16 1.95 12.00 1.97 — — — SnO 3.75 6.90 1.98 3.561.97 6.59 12.72 1.96 Cu₂O 2.97 7.32 1.03 2.81 — — — 2.05 SO₃ — — — — —0.15 0.14 — Fe₂O₃ — — — — — 0.48 — — Reducing yes yes yes yes yes yesagent* *A reducing agent such as a sugar or potassium sodium tartrate isused in the range of 0.5-20 wt %.

Example 2

The ingredients of Frit B were melted at 1400° C. for 1 hour. After afast cool-down to room temperature the fit was annealed at 550° C. untila dark red color was achieved. The frit was milled (D₉₀<16 microns).

Example 3

The ingredients of Frit C were melted at 1100° C. for 1 hour. After afast cooling down to room temperature the fit was annealed at 550° C.until a dark red color was achieved. The frit was milled (D₉₀<16microns).

Example 4

The ingredients of Frit D were melted at 1400° C. for 1 hour. After afast cooling down to room temperature the frit was annealed at 550° C.until a dark red color was achieved. The frit was milled (D₉₀<50microns).

Example 5

Ingredients of Frit E were melted at 1000° C. for 1 hour. After a fastcooling down to room temperature. The fit was milled (D₉₀<50 microns).

Example 6

Making a red pigment with a reducing flux. The following ingredientswere mixed: 49.51 grams of the product of Example 5, 12.62 grams ofCuSO₄, and 37.87 grams of Na₂SO₄. The mixture was annealed for 135minutes at 550° C., washed with hot water and filtered. The red pigmentwas milled to a D₉₀<16 microns.

Example 7

Example 6 was mixed with media and sprayed onto a steel plate which wascolored before with white enamel. The steel plate was dried and thenfired for 10 min at 700° C. An α-blood-red color was obtained on thesteel plate.

Example 8

Frit B was mixed with a fit (Ferro NPR 820) at a 1:1 weight ratio andpasted with media (Ferro 80 1022) at a 10:7 weight ratio andscreen-printed (48 mesh) on glass. The glass was fired at 650° C. for 10min. after firing, the glass samples showed a red color.

Example 9

The ingredients of Frit H were melted at 1400° C. and cooled to roomtemperature by quenching with water. The frit was heated two hours at550° C. and formed a dark red colored glass, useful as a pigment. Theglass/pigment was milled in a ball mill. The milled pigment was mixedwith a frit, Ferro NPR 820 at a 1:1 weight ratio. A screen printingmedium (Ferro 801022) at a 10:7 weight ratio (frit:medium) was mixedtherewith, to form a paste, which was printed on glass, and fired 10minutes at 640° C., the heating rate being 14K/minute. A red decoratedglass was obtained.

Example 10

The ingredients of Frit A were melted at 1400° C. for 1 hour. After afast cooling down to room temperature the frit was annealed at 550° C.until a dark red color was achieved. The fit was milled to a D₉₀<16microns.

Example 11

The product of Example 10 was mixed with flux 10 1650 (Ferro) in aweight ratio of 1:2 and pasted with media 80 820 (Ferro) in a weightratio of 1:1, printed on porcelain and fired for 10 min at 820° C., theheating rate being 7K/minute. An α-blood-red color was obtained on theporcelain.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative example shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general invention concept asdefined by the appended claims and their equivalents.

The invention claimed is:
 1. An enamel composition that is free of lead,cadmium, bismuth, iron, selenium, arsenic, tantalum, chromium andsulfides, the composition comprising a solids portion comprising a fritportion, wherein the frit portion comprises, prior to firing: a. 50-75wt % SiO₂, b. 4-22 wt % R₂O, wherein R is at least one of Na and K, c.2-30 wt % R′O, wherein R′ is at least one of Mg, Ca, Sr and Ba, d.0.5-20 wt % B₂O₃, e. 1-15 wt % SnO, and f. 2-10 wt % of at least one ofCu₂O and CuO.
 2. The composition of claim 1, wherein the frit portionfurther comprises 0.1-5 wt % Fe₂O₃.
 3. The composition of claim 1,wherein R₂O comprises 0.3-18 wt % Na₂O and sufficient K₂O to bring thetotal Na₂O+K₂O to 4-22%.
 4. The composition of claim 1, wherein the fritportion comprises, prior to firing: a. 50-70 wt % SiO₂, b. 6-20 wt %R₂O, c. 3-12 wt % CaO, d. 0-12 wt % MgO, e. 5-15 wt % B₂O₃, f. 0-12 wt %Al₂O₃, g. 2-12 wt % SnO, and h. 2-10 wt % of at least one of Cu₂O andCuO.
 5. The composition of claim 4, wherein R₂O comprises 3-15 wt % Na₂Oand sufficient K₂O to bring the total Na₂O+K₂O to 6-20%.
 6. A substratebearing a fired coating of the composition of claim
 1. 7. Thecomposition of claim 1, wherein the frit portion further comprises0.5-20 wt % of a reducing agent selected from the group consisting ofreducing sugars, potassium sodium tartrate, organic compounds, organicsalts, carbon black and combinations thereof.
 8. The composition ofclaim 1, wherein the frit portion comprises, prior to firing: a. 50-70wt % SiO₂, b. 6-20 wt % R₂O, c. 2-24 wt % R′O, d. 5-16 wt % B₂O₃, e.2-12 wt % SnO, f. 2-10 wt % of at least one of Cu₂O and CuO, and furthercomprises g. 0-12 wt % Al₂O₃.
 9. The composition of claim 1, wherein thefrit portion comprises, prior to firing: a. 50-75 wt % SiO₂, b. 4-22 wt% R₂O, wherein R is at least one of Na and K, c. 2-30 wt % R′O, whereinR′ is at least one of Mg, Ca, Sr and Ba, d. 0.5-20 wt % B₂O₃, e. 3-15 wt% SnO, and f. 2-10 wt % of at least one of Cu₂O and CuO.
 10. A method ofmaking a red glass frit pigment composition comprising a. smelting aglass by heating a mixture of compounds that provide the followingoxides: i. 50-75 wt % SiO₂, ii. 4-22 wt % R₂O, wherein R is at least oneof Na and K, iii. 2-30 wt % R′O, wherein R′ is at least one of Mg, Ca,Sr and Ba, iv. 0.5-20 wt % B₂O₃, v. 1-15 wt % SnO, and vi. 2-10 wt % ofat least one of Cu₂O and CuO, b. cooling the glass, c. annealing, toincrease the color strength, if necessary, and d. reducing the glass toa desired particle size by mechanical grinding or milling.
 11. Aparticulate red pigment composition comprising the glass frit producedby the process of claim 10, said glass frit having a D₉₀ particle sizeof less than 10 microns.
 12. A method of manufacturing red glasscomprising adding a coloring frit, to a mass of molten colorless glassin a feeder channel, forming glass objects from the molten mass ofglass, then subjecting the glass objects to heat treatment so that theydevelop a red color, wherein the coloring frit is free of lead, cadmium,bismuth, iron, selenium, arsenic, tantalum, chromium and sulfides, andwherein the coloring frit comprises: a. 50-75 wt % SiO₂, b. 4-22 wt %R₂O, wherein R is at least one of Na and K, c. 2-30 wt % R′O, wherein R′is at least one of Mg, Ca, Sr and Ba, d. 0.5-20 wt % B₂O₃, e. 1-15 wt %SnO, and f. 2-10 wt % of at least one of Cu₂O and CuO.
 13. The method ofclaim 12, wherein the partial pressure of oxygen in the molten mass ofglass is less than 10⁻⁹ atmospheres.
 14. A method of decorating athermoplastic mass, comprising a. forming a red-colored enamelcomposition enamel composition that is free of lead, cadmium, iron,bismuth, selenium, arsenic, tantalum, chromium and sulfides, thecomposition comprising a solids portion comprising a frit portion,wherein the frit portion comprises, prior to firing: b. 50-75 wt % SiO₂,c. 8-25 wt % R₂O, wherein R is at least one of Li, Na and K, d. 2-30 wt% R′O, wherein R′ is at least one of Mg, Ca, Sr and Ba, e. 1-15 wt %SnO, and f. 2-10 wt % of at least one of Cu₂O and CuO, and g. blendingthe enamel composition with a thermoplastic mass to form a red-coloredthermoplastic mass.
 15. The method of claim 12, wherein the mass ofmolten colorless glass has a partial pressure of oxygen in the moltenmass of greater than 10⁻⁴ to less than 10⁻¹ atmospheres.